Dominance of texture over shape in facial identity processing is modulated by individual abilities

Investigating the neural effects of typicality and predictability for face and object stimuli

The brain calibrates itself based on the past stimulus diet, which makes frequently observed stimuli appear as typical (as opposed to uncommon stimuli, which appear as distinctive). Based on predictive processing theory, the brain should be more "prepared" for typical exemplars, because these contain information that has been encountered frequently, allowing it to economically represent items of that category. Thus, one could ask whether predictability and typicality of visual stimuli interact, or rather act in an additive manner. We adapted the design by Egner and colleagues (2010), who used cues to induce expectations about stimulus category (face vs. chair) occurrence during an orthogonal inversion detection task. We measured BOLD responses with fMRI in 35 participants. First, distinctive stimuli always elicited stronger responses than typical ones in all ROIs, and our whole-brain directional contrasts for the effects of typicality and distinctiveness converge with previous findings. Second and importantly, we could not replicate the interaction between category and predictability reported by Egner et al. (2010), which casts doubt on whether cueing designs are ideal to elicit reliable predictability effects. Third, likely as a consequence of the lack of predictability effects, we found no interaction between predictability and typicality in any of the four tested regions (bilateral fusiform face areas, lateral occipital complexes) when considering both categories, nor in the whole brain. We discuss the issue of replicability in neuroscience and sketch an agenda for how future studies might address the same question.

Differences between high and low performers in face recognition in electrophysiological correlates of face familiarity and distance-to-norm

Valentine's influential norm-based multidimensional face-space model (nMDFS) predicts that perceived distinctiveness of a face increases with its distance to the norm. Occipito-temporal event-related potentials (ERPs) have been recently shown to respond selectively to variations in distance-to-norm (P200) or familiarity (N250, late negativity), respectively (Wuttke & Schweinberger, 2019). Despite growing evidence on interindividual differences in face perception skills at the behavioral level, little research has focused on their electrophysiological correlates. To reveal potential interindividual differences in face spaces, we contrasted high and low performers in face recognition in regards to distance-to-norm (P200) and familiarity (N250). We replicated both the P200 distance-to-norm and the N250 familiarity effect. Importantly, we observed: i) reduced responses in low compared to high performers of face recognition, especially in terms of smaller distance-to-norm effects in the P200, possibly indicating less 'expanded' face spaces in low compared to high performers; ii) increased N250 responses to familiar original faces in high performers, suggesting more robust face identity representations. In summary, these findings suggest the contribution of both early norm-based face coding and robust face representations to individual face recognition skills, and indicate that ERPs can offer a promising route to understand individual differences in face perception and their neurocognitive correlates.

Testing stimulus exposure time as the critical factor of increased EPN and LPP amplitudes for fearful faces during perceptual distraction tasks

Fearful facial expressions are prioritized across different information processing stages, as evident in early, intermediate, and late components of event-related brain potentials (ERPs). Recent studies showed that, in contrast to early N170 modulations, mid-latency (Early Posterior Negativity, EPN) and late (Late Positive Potential, LPP) emotional modulations depend on the attended perceptual feature. Nevertheless, several studies reported significant differences between emotional and neutral faces for the EPN or LPP components during distraction tasks. One cause for these conflicting findings might be that when faces are presented sufficiently long, participants attend to task-irrelevant features of the faces. In this registered report, we tested whether the presentation duration of faces is the critical factor for differences between reported emotional modulations during perceptual distraction tasks. To this end, 48 participants were required to discriminate the orientation of lines overlaid onto fearful or neutral faces, while face presentation varied (100 msec, 300 msec, 1,000 msec, 2,000 msec). While participants did not need to pay attention to the faces, we observed main effects of emotion for the EPN and LPP, but no interaction between emotion and presentation duration. Of note, unregistered exploratory tests per presentation duration showed no significant EPN and LPP emotion differences during short durations (100 and 300 msec) but significant differences with longer durations. While the presentation duration seems not to be a critical factor for EPN and LPP emotion effects, future studies are needed to investigate the role of threshold effects and the applied analytic designs to explain conflicting findings in the literature.

Are estimates of faces' ages less accurate when they wear sunglasses or face masks and do these disguises make it harder to later recognise the faces when undisguised?

This study examined whether our ability to accurately estimate unfamiliar faces’ ages declines when they are wearing sunglasses or surgical-style face masks and whether these disguises make it harder to later recognise those faces when undisguised. In theory, both disguises should harm age estimation accuracy and later face recognition as they occlude facial information that is used to determine a face’s age and identity. To establish whether this is the case, we had participants estimate the age of unfamiliar faces that were pictured wearing no disguises, sunglasses, or face masks. The participants then completed a face recognition test where they had to distinguish between the previously seen faces and new faces. Importantly, none of faces wore disguises in this latter test. Participants’ estimates of the undisguised faces’ ages were inaccurate by a Median of 5.15 years. Their accuracy barely changed when the faces wore sunglasses but declined by a Median of 1.30 years when they wore face masks. Moreover, subsequent undisguised face recognition was less likely to occur when the faces previously wore sunglasses or face masks, with large effects observed. These findings demonstrate the relative importance of different facial areas when estimating faces’ ages and later recognising them. They also have implications for policing as they suggest it may be harder for eyewitnesses to accurately estimate the age of criminals who wear face masks during offences, and it may be harder for them to later recognise criminals in line-ups if the criminals wear sunglasses or face masks during offences.

The influence of visual distortion on face recognition

A person's ability to recognise familiar faces is critical to their participation in many aspects of society. Following an acquired brain injury or retinal disease, however, faces can appear distorted, a phenomenon known as prosopometamorphopsia. Although case reports have described a variety of changes in the appearance of faces during prosopometamorphopsia, the influence of the disorder on face recognition has not been rigorously investigated. In the present report, we quantify how well healthy observers can recognise familiar faces that have been distorted using a parametric model of prosopometamorphopsia. Our results reveal that face recognition varies systematically with the parameters of visual distortion, which, importantly, interact with the size of the face in a nonlinear but highly predictable manner. Our findings demonstrate that prosopometamorphopsia can lead to a surprising range of changes in the appearance of faces. The impact of visual distortion on face recognition thus depends critically on the distance at which the face is viewed, which is likely to change across social and clinical contexts.

The role of stimulus-based cues and conceptual information in processing facial expressions of emotion

Face shape and surface textures are two important cues that aid in the perception of facial expressions of emotion. Additionally, this perception is also influenced by high-level emotion concepts. Across two studies, we use representational similarity analysis to investigate the relative roles of shape, surface, and conceptual information in the perception, categorisation, and neural representation of facial expressions. In Study 1, 50 participants completed a perceptual task designed to measure the perceptual similarity of expression pairs, and a categorical task designed to measure the confusability between expression pairs when assigning emotion labels to a face. We used representational similarity analysis and constructed three models of the similarities between emotions using distinct information. Two models were based on stimulus-based cues (face shapes and surface textures) and one model was based on emotion concepts. Using multiple linear regression, we found that behaviour during both tasks was related with the similarity of emotion concepts. The model based on face shapes was more related with behaviour in the perceptual task than in the categorical, and the model based on surface textures was more related with behaviour in the categorical than the perceptual task. In Study 2, 30 participants viewed facial expressions while undergoing fMRI, allowing for the measurement of brain representational geometries of facial expressions of emotion in three core face-responsive regions (the Fusiform Face Area, Occipital Face Area, and Superior Temporal Sulcus), and a region involved in theory of mind (Medial Prefrontal Cortex). Across all four regions, the representational distances between facial expression pairs were related to the similarities of emotion concepts, but not to either of the stimulus-based cues. Together, these results highlight the important top-down influence of high-level emotion concepts both in behavioural tasks and in the neural representation of facial expressions.

Similar use of shape and texture cues for own- and other-race faces during face learning and recognition

Although the other-race effect (ORE; superior recognition of own- relative to other-race faces) is well established, the mechanisms underlying it are not well understood. We examined whether the ORE is attributable to differential use of shape and texture cues for own- vs. other-race faces. Shape cues are particularly important for detecting that an own-race face is unfamiliar, whereas texture cues are more important for recognizing familiar and newly learned own-race faces. We compared the influence of shape and texture cues on Caucasian participants' recognition of Caucasian and East Asian faces using two complementary approaches. In Experiment 1, participants studied veridical, shape-caricatured, or texture-caricatured faces and then were asked to recognize them in an old/new recognition task. In Experiment 2, all study faces were veridical and we independently removed the diagnosticity of shape (or texture) cues in the test phase by replacing original shape (or texture) with average shape (or texture). Despite an overall own-race advantage, participants' use of shape and texture cues was comparable for own- and other-race faces. These results suggest that the other-race effect is not attributable to qualitative differences in the use of shape and texture cues.

Effects of low-level visual information and perceptual load on P1 and N170 responses to emotional expressions

Emotional facial expressions lead to modulations of early event-related potentials (ERPs). However, it has so far remained unclear how far these modulations represent face-specific effects rather than differences in low-level visual features, and to which extent they depend on available processing resources. To examine these questions, we conducted two preregistered independent experiments (N = 40 in each experiment) using different variants of a novel task that manipulates peripheral perceptual load across levels but keeps overall visual stimulation constant. At the display center, we presented task-irrelevant angry, neutral, and happy faces and their Fourier phase-scrambled versions, which preserved low-level visual features. The results of both studies showed load-independent P1 and N170 emotional expression effects. Importantly, by using Bayesian analyses we could confirm that these facial expression effects were face-independent for the P1 but not for the N170 component. We conclude that firstly, ERP modulations during the P1 interval strongly depend on low-level visual information, while the N170 modulation requires the processing of figural facial expression features. Secondly, both P1 and N170 modulations appear to be immune to a large range of variations in perceptual load.

Contrast Negation Impairs Sorting Unfamiliar Faces by Identity: A Comparison With Original (Contrast-Positive) and Stretched Images

Recognition of unfamiliar faces is difficult in part due to variations in expressions, angles, and image quality. Studies suggest shape and surface properties play varied roles in face learning, and identification of unfamiliar faces uses diagnostic pigmentation/surface reflectance relative to shape information. Here, participants sorted photo-cards of unfamiliar faces by identity, which were shown in their original, stretched, and contrast-negated forms, to examine the utility of diagnostic shape and surface properties in sorting unfamiliar faces by identity. In four experiments, we varied the presentation order of conditions (contrast-negated first or original first with stretched second across experiments) and whether the same or different photo-cards were seen across conditions. Stretching the images did not impair performance in any measures relative to other conditions. Contrast negation generally exacerbated poor sorting by identity compared with the other conditions. However, seeing the contrast-negated photo-cards last mitigated some of the effects of contrast negation. Together, results suggest an important role for surface properties such as pigmentation and reflectance for sorting by identity and add to literatures on informational content and appearance variability in discrimination of facial identity.

Facial Identification at a Virtual Reality Airport

Person identification at airports requires the comparison of a passport photograph with its bearer. In psychology, this process is typically studied with static pairs of face photographs that require identity-match (same person shown) versus mismatch (two different people) decisions, but this approach provides a limited proxy for studying how environment and social interaction factors affect this task. In this study, we explore the feasibility of virtual reality (VR) as a solution to this problem, by examining the identity matching of avatars in a VR airport. We show that facial photographs of real people can be rendered into VR avatars in a manner that preserves image and identity information (Experiments 1 to 3). We then show that identity matching of avatar pairs reflects similar cognitive processes to the matching of face photographs (Experiments 4 and 5). This pattern holds when avatar matching is assessed in a VR airport (Experiments 6 and 7). These findings demonstrate the feasibility of VR as a new method for investigating face matching in complex environments.

Temporal Contiguity Training Influences Behavioral and Neural Measures of Viewpoint Tolerance

Humans can often recognize faces across viewpoints despite the large changes in low-level image properties a shift in viewpoint introduces. We present a behavioral and an fMRI adaptation experiment to investigate whether this viewpoint tolerance is reflected in the neural visual system and whether it can be manipulated through training. Participants saw training sequences of face images creating the appearance of a rotating head. Half of the sequences showed faces undergoing veridical changes in appearance across the rotation (non-morph condition). The other half were non-veridical: during rotation, the face simultaneously morphed into another face. This procedure should successfully associate frontal face views with side views of the same or a different identity, and, according to the temporal contiguity hypothesis, thus enhance viewpoint tolerance in the non-morph condition and/or break tolerance in the morph condition. Performance on the same/different task in the behavioral experiment (N = 20) was affected by training. There was a significant interaction between training (associated/not associated) and identity (same/different), mostly reflecting a higher confusion of different identities when they were associated during training. In the fMRI study (N = 20), fMRI adaptation effects were found for same-viewpoint images of untrained faces, but no adaptation for untrained faces was present across viewpoints. Only trained faces which were not morphed during training elicited a slight adaptation across viewpoints in face-selective regions. However, both in the behavioral and in the neural data the effects were small and weak from a statistical point of view. Overall, we conclude that the findings are not inconsistent with the proposal that temporal contiguity can influence viewpoint tolerance, with more evidence for tolerance when faces are not morphed during training.

Familiar Face Priming: The Role of Second-Order Configuration and Individual Face Recognition Abilities

The role of second-order configuration-that is, metric distances between individual features-for familiar face recognition has been the subject of debate. Recent reports suggest that better face recognition abilities coincide with a weaker reliance on shape information for face recognition. We examined contributions of second-order configuration to familiar face repetition priming by manipulating metric distances between facial features. S1 comprised familiar face primes as either: unaltered, with increased or decreased interocular distance, with increased or decreased distance between nose and mouth; or a different familiar face (unprimed). Participants performed a familiarity decision task on familiar and unfamiliar S2 targets, and completed a test battery consisting of three face identity processing tests. Accuracies, reaction times, and inverse efficiency scores were assessed for the priming experiment, and potential priming costs in inverse efficiency scores were correlated with test battery scores. Overall, priming was found, and priming effects were reduced only by primes with interocular distance distortions. Correlational data showed that better face recognition skills coincided with a weaker reliance on second-order configurations. Our findings (a) suggest an importance of interocular, but not mouth-to-nose, distances for familiar face recognition and (b) show that good face recognizers are less sensitive to second-order configuration.